Yield impacts on the concentration of aroma precursors in grapevine berries (Vitis vinifera L.)

Abstract

Volatile aroma compounds in grapes are found either as free and as glycoconjugated molecule. Glycosylated aroma precursors belong mainly to four compounds families: non terpenic alcohols, phenols, terpenes and norisoprenoids. Up to date there is little information about how the accumulation of aromatic compounds is regulated in relation to C balance changes at plant level. The aim of this project was to study the relationship between fruit load, as a mean to modify the balance of C assimilates within vegetative and reproductive organs, and the accumulation of glycosylated aroma precursors. Experiments were performed in 2015 and 2016 seasons at the experimental research unit of INRA Pech-Rouge (South of France) under Mediterranean climate. Two varieties were experimented: Schiraz and Muscat à Petit Grains. Plants were thinned up to 50 % or 70 % by removing bunches at two phenological stages: pea-size (rapid growth stage) and onset of ripening. Samples were collected at 2 (Schiraz) or 5 (Muscat) dates around ripening stage. Analyses consisted in measuring berry weight and volume, sugars, tartaric and malic acid, and anthocyanins concentration; pH and IPT (polyphenolic content index). Aroma precursors were quantified by gaseous chromatography (GC-MS). LSD Fisher test for p < 0.05 was used to evaluate the existence of significant dif­ferences by ANOVA. Results showed that the aroma precursors were positively affected by cluster thinning in Schiraz, mainly when thinning was made at pea-size stage compared to control plants and even with those thinned at veraison. In contrast, we found that Muscat berries from plants thinned at the onset of ripenning showed an increment of total glycosylated aroma precursors.